Much of the research described here was supported by the Institute of Education Sciences, U.S. Department of Education, through Grant R305A080621 to Vanderbilt University (Laura R. Novick, PI; Kefyn M. Catley, Co-I). The opinions expressed are those of the authors and do not represent views of the Institute or the U.S. Department of Education.Instructional Materials Available for Download
As part of the above-mentioned IES grant, we have developed a variety of instructional materials for teaching tree thinking to undergraduates. Some of these materials are available for download here. The first is a self-study instructional booklet (e.g., can be assigned for homework). Versions of this booklet have been used by, and found effective for, (a) students of varying backgrounds recruited from a psychology subject pool, (b) students enrolled in an introductory biology course for science majors, and (3) biology majors enrolled in an upper-level biology class. The second is a phylogenetics laboratory activity for use in biology classes. The third is the instructor's guide and answer key for the laboratory. The laboratory has been used with the second two populations mentioned in conjunction with the instructional booklet. A manuscript reporting this research is in preparation (Novick, Catley, & Schreiber, 2013).
Novick, L. R., Catley, K. M., & Schreiber, E. G. (2012). Understanding Evolutionary History: An Introduction to Tree Thinking (version 3.2). Unpublished instructional booklet, Department of Psychology and Human Development, Vanderbilt University, Nashville, TN. (Click to dowload the instructional booklet.)
Catley, K. M., & Novick, L. R. (2012). Phylogenetics Laboratory: Reconstructing Evolutionary History (version 3.2).Unpublished student laboratory booklet, Department of Psychology and Human Development, Vanderbilt University, Nashville, TN. (Click to dowload the laboratory booklet.)
Catley, K. M., & Novick, L. R. (2012). Phylogenetics Laboratory: Reconstructing Evolutionary History Instructors' Guide and Answer Key (version 2.2). Unpublished laboratory instructors' guide, Department of Psychology and Human Development, Vanderbilt University, Nashville, TN. (Click to dowload the laboratory instructor's guide and answer key.)
Hear About a Recent Project in Our Lab
Click below to listen to a presentation (approximately an hour) of some our research (Novick, Catley, & Funk, 2011).
Abstract diagrams are important not only in mathematics but in science as well (Novick, 2006). In biology, hierarchical diagrams are especially common. For the past 9 years, I have been working with Kefyn Catley, an evolutionary biologist and science educator, to investigate college and high school students' understanding of cladograms, the most important tool that contemporary scientists use to reason about evolutionary relationships. A cladogram is a type of hierarchical diagram that depicts hypotheses about nested sets of taxa that are supported by shared, evolutionarily novel characters called synapomorphies. For example, the cladogram shown at the top of the page indicates that one synapomorphy for birds and alligators is that they both possess a gizzard. That is, birds and alligators share a most recent common ancestor (MRCA) that evolved the novel character of possessing a gizzard. A group of taxa consisting of the MRCA and all descendants of that ancestor is called a clade or monophyletic group. Thus, birds and alligators comprise a clade (in the cladogram shown above). Because of the nesting inherent in hierarchical diagrams, birds, alligators, and lizards also comprise a clade. And those three taxa plus mammals (represented by manatees and elephants in the cladogram above) constitute another clade, etc. The synapomorphy supporting the bird/alligator clade distinguishes the MRCA of birds and alligators from the earlier ancestor common to birds, alligators, and lizards. And the synapomorphy supporting the bird/alligator/lizard clade (see UV light) distinguishes the MRCA of those three taxa from the earlier ancestor common to birds, alligators, lizards, and mammals. The latter ancestor evolved the novel character of having an amniotic egg, a critical development in the history of life on Earth that enabled vertebrates possessing this character to complete their life cycles on land.
Biologists use the tool of phylogenetics along with its product, the cladogram, to study macroevolution, the subdiscipline of biology that synthesizes events of Earth history and deep time (the well-established theory that Earth is billions of years old) with mechanisms that generate and maintain the biodiversity of our planet. Macroevolutionary processes operate at the level of species and above, resulting in the formation, radiation, and extinction of higher groups of taxa. Macroevolution explains, for example, both the origin and radiation of mammalian taxa. In contrast, microevolution concerns processes that occur at the level of the organism (i.e., genome, individual, and population). Microevolution explains, for example, the appearance of antibiotic-resistant strains of bacteria.
Cladograms are the most important tool used by evolutionary biologists because they document and organize existing knowledge about the properties of species and higher-order taxa. By invoking monophyly to systematize the 3.5 billion year history of life on Earth, they (a) enable evidence-based inference and (b) provide a conceptual framework for basic and applied biology.
A number of researchers have recently been calling for the inclusion of tree thinking in biology curricula from middle school through the undergraduate years. Tree thinking is the ability to understand and reason with evolutionary relationships depicted in cladograms (phylogenetic trees). The power of tree thinking is that the resulting classification scheme -- for example that alligators are more closely related to birds than to lizards because of their shared MRCA -- reflects current understanding of the history of life on Earth (i.e., the evolutionary relationships among taxa). Thus, inferences based on this classification scheme are likely to be more informative and to have greater practical value than inferences based on other criteria. For example, inferring which antivenin to use to counteract the bite of a venomous king brown snake based on its close evolutionary relationship to the red-bellied black snake is more likely to lead to a successful outcome (survival!) than basing the choice of antivenin on the king brown snake's similar appearance to the western brown snake.
Implementing tree thinking in biology curricula is consistent with the Next Generation Science Standards, which expect students to acquire proficiency in using the methodologies and tools from professional practice (National Research Council, 2013).
Summary of Our Research
Overview. Our research on tree thinking falls into three broad categories: (a) Influences of diagram design on interpretations of evolutionary relationships, (b) assessing and improving students' tree-thinking skills, and (c) effects of prior knowledge about taxonomic relationships on tree thinking. Studies in the first group have a primarily cognitive psychological basis, with strong implications for education. Studies in the second group are rooted in science education while being informed by cognitive psychology. Studies in the third group reflect a more even mix of psychological and educational foundations. All studies are informed by expert knowledge of evolutionary biology. We have used a variety of different kinds of tasks, including those that require diagram comprehension, translation from one diagram format to another, and inference. Our measures of performance include accuracy, types of errors made, written explanations (evidence cited) in support of one's responses, and patterns of eye movements.
Influences of diagram design on interpretations of evolutionary relationships. Consistent with a large cognitive psychological literature on diagram comprehension, we would expect students' interpretations of diagrams depicting evolutionary relationships to be influenced by how those diagrams are designed. Thus, one major focus of our research program has been to discover how diagram design affects students' interpretations of a variety of different types of tree-of-life representations.
One project compared students' ability to extract the hierarchical structure from cladograms depicted in different ways. Cladograms are typically drawn in one of two formats: rectangular trees (left diagram in the figure below) and diagonal ladders (right diagram in the figure below). In an analysis of the cladograms printed in a professional journal, Novick and Catley (2007) found that rectangular trees are by far the preferred format among evolutionary biologists: 83% vs. 17%. In high school and biology textbooks, however, the diagonal format was found to occur slightly more often than the rectangular format: 59% vs. 41% for high school biology texts and 54% vs. 46% for college texts (Catley & Novick, 2008).
In an initial set of two studies, we investigated college students' ability to translate between the diagonal and rectangular formats for drawing cladograms. We found that students particularly had trouble understanding the structure of the diagonal format, and this difficulty was especially pronounced for students with weaker backgrounds in biology. We hypothesized that this difficulty stems from the Gestalt principle of good continuation, which makes it difficult to extract the critical information about hierarchical levels from diagonal format cladograms. Examination of the errors students made in drawing diagonal format cladograms and in translating from the diagonal to the rectangular format supported this hypothesis. A preliminary report of this research may be found in Novick and Catley (2006); the full report is in Novick and Catley (2007).
One implication of our results concerning the primary cause of students' difficulty in understanding the diagonal cladogram format is that if some method can be found to break good continuation at the appropriate points along the continuous lines, students' ability to correctly extract the hierarchical structure of diagonal cladograms should improve. The method we tested was to add a synapomorphy to mark each branching point in such cladograms. As reported in Novick, Catley, and Funk (2010), this manipulation greatly improved students' ability to translate diagonal cladograms to the rectangular format. Thus, Kefyn and I used this experimental task in the college-level tree-thinking curriculum we developed to help students understand the diagonal format.
We are excited to report that based on this research, four college biology textbooks have changed from depicting cladograms in the diagonal to the rectangular format: (a) Freeman, S. (2011). Biological Science (4th ed.). Boston, MA: Benjamin Cummings. (b) Raven, P. H., Johnson, G. B., Mason, K. A., Losos, J., & Singer, S. (2014). Biology (10th ed.). Boston, MA: McGraw-Hill. (c) Hickman, C. P. Jr., Keen, S. L., Larson, A., & Eisenhour, D. J. (2011). Integrated Principles of Zoology (15th ed.). Boston, MA: McGraw-Hill. (d) Bergstrom, C. T., & Dugatkin, L. A. (2011). Evolution. New York, NY: Norton.
More recently, we used eye-tracking methodology to uncover two additional factors that affect college students' ability to correctly extract the hierarchical structure of cladograms depicted in the diagonal format and to translate that structure to the rectangular format (Novick, Stull, & Catley, 2012). One factor is students' strong bias to scan cladograms from left to right, following their highly practiced directional pattern for reading written text. The second factor is their preference to scan along the main diagonal line at the base of the diagonal cladogram. These two factors in combination mean that students scan diagonal cladograms such as that shown in the above figure from left to right and from bottom to top, which impairs their ability to uncover the correct pattern of nesting. If the diagrams are simply reflected so that the main diagonal runs from the top left to the bottom right of the cladogram (a seemingly trivial design factor), students scan from left to right and from top to bottom, which facilitates joining taxa to reflect the correct pattern of nesting. Thus, students were more successful in translating diagonal cladograms to the rectangular format when they were presented in the latter than the former orientation. Two biology professors showed the same pattern of results. The diagonal cladogram orientation shown in the figure above is the canonical representation used in textbooks and in the biology literature.
A second project on the effects of diagram design examined students' understanding of tree-of-life diagrams that are not cladograms (Catley, Novick, & Shade, 2010; Novick, Shade, & Catley, 2011). Such diagrams, although they are commonly found in high school and college textbooks (Catley & Novick, 2008), appear to be poorly conceived and may reinforce evolutionary misconceptions. We wanted to determine whether the information extracted from such diagrams is in accordance with contemporary understanding of evolutionary theory. Our analyses documented persistent misconceptions that fall broadly into two categories: (a) Evolution as an anagenetic rather than a cladogenetic process and (b) evolution as a teleological (purpose-driven) process. Cladogenesis, the accepted means of speciation, is a process whereby one species splits into two when the population of a parent species is fragmented, and selection continues separately in each group driven by the pressures of each local environment. Anagenesis, in contrast, is a process whereby one species evolves directly into (i.e., becomes) another species over time without any branching events. There is no evidence to support anagenesis as a mechanism of speciation. In a follow-up study conducted by Courtney Shade for her honors project, we compared students' responses to evolutionary relationship questions when they accompanied cladograms (in the rectangular and diagonal formats) versus other evolutionary diagrams often seen in textbooks. As predicted, we found that the textbook diagrams, which contained linear components, were more likely than the two cladogram formats to yield explanations of speciation as an anagenetic process. In contrast, the branching cladogram formats yielded more appropriate interpretations in terms of levels of ancestry than did the textbook diagrams.
In a final project on diagram design, we rotated the branches of rectangular format cladograms to change the left-to-right order of the taxa at the branch tips, which does not change the structure of the evolutionary relationships depicted, and examined the effect of this manipulation on students' interpretations of the evolutionary relationships depicted. For example, consider the cladogram at the top of this page. If the branches were rotated at the point indicated by the synapomorphy amniotic egg, the two mammals (manatee and elephant) would move to the middle of the diagram and the lizard would move to the far right location, without altering the pattern of connections among the taxa. If the cladogram were oriented vertically rather than horizontally, a similar rotation would move the mammals from the top to the middle and the lizard from the middle to the top. In two studies, we examined college and high school students' propensity to state that humans (versus honeybees) are the most highly evolved taxon when they occupied an end (far right or top) versus middle position in the cladogram (Phillips, Novick, & Catley, 2013). Both age groups were quite likely to incorrectly say that humans are the most highly evolved taxon of those depicted in the cladogram but highly unlikely to make the same claim about honeybees, even though those two taxa were similarly situated in their cladograms. This finding replicates earlier research on students' misconceptions about human evolution. From a diagram design perspective, the more interesting result is that for the cladogram that included humans, students were more likely to say that taxon is most highly evolved when it occupied an end rather than a middle position in the cladogram. Unfortunately, cladograms in textbooks tend to reinforce this misconception about human evolution: When cladograms include humans, that taxon is almost always placed at the far right or top of the cladogram (depending on whether the cladogram is presented in a horizontal or vertical orientation).
Assessing and improving students' tree-thinking skills. Documenting students' tree-thinking skills based on naturally-occurring instruction in college and high school biology classes is a critical first step for developing new curricula to improve students' ability to engage in this important 21st century skill. Accordingly, a second major focus of our research program concerns students' ability to engage in tree thinking. We are both assessing existing tree-thinking skills and developing new curricula for both college and high school students.
Our first study investigated college students' ability to comprehend and reason from cladograms in both the rectangular and diagonal formats, such as those depicted in the figure immediately above (Novick & Catley, 2013a). In this study, students answered questions such as: (a) "What character was possessed by the most recent common ancestor of lizards and mammals?" [answer is amniotic egg], (b) "Which taxa did not evolve from an ancestor that had lungs?" [answer is lobsters, spiders, perch, and flounder], and (c) "Are lungfish more closely related to mammals or to flounder? What evidence supports your answer?" [answer is mammals because lungfish share a more recent common ancestor with mammals than they do with flounder].
We examined both accuracy and students' justifications to gain insight into their understanding of and ability to reason from cladograms. Briefly, we found that students with a stronger background in biology did better than those with a weaker biology background on all of our core categories of tree-thinking questions. For the simplest questions -- identify characters (a) and identify taxa (b), for which students just had to read information off the cladograms, the difference between the two groups was larger for the diagonal format than for the rectangular format. For the more difficult relationship (c) and inference questions, the biology background difference was consistent across all other manipulations. In general, the stronger background students did better in terms of both accuracy and quality of supporting evidence cited. Replicating the results of Novick and Catley (2007), this study also found poorer performance when the evolutionary relationships were depicted in the diagonal than the rectangular format. Except for the easiest question types, even stronger background students found the diagonal format more difficult to understand than the rectangular format. Several cognitive and perceptual factors were found to affect students' performance, including, for example, the Gestalt principle of good continuation and whether the question was worded affirmatively or negatively. Finally, a composite tree-thinking score that quantified the extent to which students cited evidence concerning most recent common ancestry to support their answers indicated that even stronger background students did poorly: Mean of 0.31 (0-1 scale) for all stronger background students reasoning about information depicted in the rectangular format and mean of 0.45 for the subset of those students who had taken 4-7 potentially relevant courses.
Follow-up studies have extended this research in two directions. As a prelude to developing an empirically based tree-thinking curriculum for college students, we examined the effects of naturally-occurring instruction in phylogenetics in zoology and evolution classes on students' success at answering a variety of tree-thinking questions (Catley, Novick, & Funk, 2012; Phillips, Novick, Catley, & Funk, 2012). Second, to inform our adaptation of the undergraduate curriculum for use with high school students, we collected data on tenth-graders' ability to engage in tree thinking (Catley, Phillips, & Novick, in press).
We are currently engaged in a major effort to design effective tree-thinking curricula for both college and high school students. We have conducted three studies evaluating our novel tree-thinking curriculum for college students, which are described in the next several paragraphs. A manuscript reporting the development of our college curriculum and associated assessment instrument, as well as the results of our implementation studies, is currently in preparation (Novick et al., 2013). Because of serious validity issues with the only published macroevolution assessment instrument (Novick & Catley, 2012), we developed our own tree-thinking assessment for our curriculum studies. In the spring of 2012, we conducted an initial test of a high school version of our curriculum in 10th grade biology classes in a rural high school in western North Carolina. Data analysis from that study is on-going.
Based on what we have learned from our experimental research, we wrote a tree-thinking instructional booklet that college students can work through at their own pace, typically taking about 30 minutes to complete the booklet. A laboratory test of this instruction was conducted by Emily Schreiber for her honors project. We found a significant effect of condition (instruction vs. no instruction) for five of the seven tree-thinking measures. A Cohen's d of 1.42 for the core tree-thinking skills composite measure indicated a large overall effect of instruction. Although there was no delay between completing the instructional booklet and taking the test, students were not allowed to refer back to the instructional booklet to answer the test questions. Another way to evaluate the effectiveness of our instructional booklet is to compare the results for this condition to those found in two of our earlier studies involving stronger biology background students in an evolution or zoology class who received two days of phylogenetics instruction in that class, after which cladograms were used throughout the remaining lectures to illustrate the macroevolutionary concepts being conveyed (Catley et al., 2012; Phillips et al., 2012). To ensure comparability of the student samples, we restricted this comparison to the results for just the stronger background students in the present study. For two types of tree-thinking questions, our self-paced instructional booklet led to comparable performance as the lengthier classroom instruction. For two additional types of tree-thinking questions, our instructional booklet led to better performance. This was especially the case for the very difficult polytomy evolutionary relationship questions.
Given these promising results, in the spring of 2010 we conducted a classroom study in the second semester of the introductory biology class for science majors at Western Carolina University. The enhanced tree-thinking instruction condition consisted of a revision of the self-paced instructional booklet, two days of lecture (taught by Kefyn), and a phylogenetics laboratory we wrote for the laboratory portion of the course. The business-as-usual instruction condition consisted of the phylogenetics laboratory we wrote and whatever material on phylogenetics the instructor chose to cover in the lecture portion of the course. Because students in the business-as-usual condition did not receive a heavy dose of phyogenetics in lecture, we judged it unwise to announce the posttest in advance. We expected those students would complain about being tested on material that might not have been covered. Accordingly, the posttest for students in both conditions was unannounced. Because students were prevented from studying for this test, their scores were lower than they otherwise would have been. Nevertheless, it is possible to look for a difference between the two instructional conditions in the amount of improvement from pretest to posttest. Statistical analyses confirmed the superiority of our enhanced tree-thinking instruction over business-as-usual instruction: (a) Students who received our enhanced instruction had higher scores than did students who received business-as-usual instruction. (b) Students did better on the posttest than on the pretest. (c) The improvement from pretest to posttest was larger for students in the enhanced instruction condition than for those in the business-as-usual condition. The difference in the amount of improvement yielded a Cohen's d = 0.59, which represents a medium size effect for the increased effectiveness of our enhanced tree-thinking instruction relative to business-as-usual. For the enhanced instruction condition alone, Cohen's d is 1.10 based on the means and standard deviations for the pretest and posttest scores and 1.45 taking into account the correlation (r = 0.37) between pretest and posttest. In either case, this represents a large effect of our enhanced tree-thinking instruction despite the fact that students were unable to study for the posttest.
We implemented a more advanced version of this curriculum in the fall of 2010 and the fall 2012 in Kefyn's Biology of Arthropods class at Western Carolina University. The instruction, which occurred during the first four weeks of the semester, consisted of a further revision of the instructional booklet, additional days of instruction during the lecture portion of the class, a revision of the phylogenetics laboratory used in the introductory biology class (Study 2), additional laboratory and homework activities, instruction in how to interpret cladograms in the more difficult diagonal format, and field work. The 17 students in this class across the two semesters combined completed our revised tree-thinking assessment before instruction began and then again a few weeks after midterm. Most questions on the assessment, like all the questions on the assessments used in Studies 1 and 2, concerned evolutionary relationships depicted in the rectangular format. A smaller number of questions concerned evolutionary relationships depicted in the diagonal format so that we could gauge the effectiveness of our instruction concerning how to interpret hierarchical structure in that format.
Focusing first on the questions asked about relationships depicted in the rectangular format, our analyses revealed that students improved from pretest to posttest for seven of the eight tree-thinking skills tested and for the composite tree-thinking measure computed across all eight skills. Cohen's d for the composite measure is 2.13 based on the means and standard deviations for the pretest and posttest scores and 2.65 taking into account the correlation (r = 0.35) between pretest and posttest. This is a large, educationally meaningful effect. We also computed separate composite tree-thinking measures for the comparable questions asked about cladograms in the rectangular and diagonal formats. Analysis of these data revealed that (a) students received significantly higher tree-thinking scores when the questions were asked about relationships depicted in the rectangular than the diagonal format, (b) students received significantly higher tree-thinking scores on the posttest than on the pretest, and (c) there was no interaction between cladogram format and time of test, indicating that our instruction in how to interpret the diagonal format did not reduce the decrement in tree-thinking skill associated with having to reason about relationships depicted in that format. In fact, the trend was for the improvement from pretest to posttest to be greater for rectangular than diagonal format questions. In our manuscript (Novick et al., 2013), we also report more qualitative indicators of the positive effect of our tree-thinking instruction on students' learning.
In sum, we set out to create, implement, and test a research-based tree-thinking curriculum and assessment instrument. Our efforts were very successful with students from a wide variety of biology backgrounds, ranging from little or no biology coursework in college to extensive biology coursework consistent with being a senior biology major. Over three connected and iterative studies, we were able to show that direct instruction produced skills that transferred to regular classroom practices and lab settings and appeared to enhance student understanding of macroevolutionary patterns and processes.
Effects of prior knowledge about taxonomic relationships on tree thinking. A third major focus of our research program is to investigate students' folkbiological knowledge about taxonomic relationships among living things and the impact of such knowledge on their ability to engage in tree thinking. This research is ongoing. An early project examined college students' knowledge of (a) the evolutionary relationships among frogs, lizards, and mammals and (b) convergent evolution (Morabito, Catley, & Novick, 2010). Although students usually group lizards together with frogs in the folkbiological category of reptiles and amphibians, lizards are in fact more closely related to mammals because those taxa share a MRCA that evolved the novel character of possessing an amniotic egg (see the cladogram at the top of the page). An alternative explanation to a shared MRCA for two taxa possessing the same character (e.g., warm-bloodedness for birds and mammals) is convergent (independent) evolution. Students often believe that taxa whose shared character is the result of convergent evolution (e.g., body shape for sharks and dolphins) are instead closely related.
Several recent projects explored these ideas in more detail. Novick, Catley, & Funk (2011) examined the extent to which misconceptions about relationships among triplets of taxa (e.g., lizards, frogs, and mammals) can be overcome by presenting simple three-taxon statements depicting the correct evolutionary relationships. Our results indicated that such diagrammatic depictions were more effective when presented in the rectangular than the diagonal format and for students who had taken introductory biology for biology majors. Even three-taxon statements in the rectangular format, however, were not always successful in overcoming students' misconceptions.
The difficulty of persuading students of the inaccuracy of their prior knowledge may relate in part to the length of time over which their misconceptions have been reinforced. Brenda Phillips (a former postdoctoral fellow in my laboratory), Tesa Dean (a former undergraduate researcher in my laboratory), Kefyn, and I recently completed data collection for an investigation of pre-K through 6th grade children's knowledge of relationships among sets of three familiar taxa (e.g., camels, elephants, and zebras; beavers, snakes, and frogs), as well as their ability to use the nesting depicted in cladograms to reason about such relationships. A comparison group of college students also completed our study. For example, consider the following question: "Think about beavers, snakes, and frogs. Which do you think are more closely related: snakes and beavers or snakes and frogs?" This question was accompanied by the three pictures shown below. One intriguing finding from this project concerns the similarity in accuracy rates in the no cladogram control condition for K-1st grade, 4th-6th grade, and college students. A second intriguing finding concerns the extent to which the explanations provided for answers to the relationship questions by these three groups of students are distinguishable, or not. For example, most students in all age groups responded, incorrectly, that snakes and frogs are more closely related. See if you can figure out the age group from which the student providing each of the following three explanations for this response came: (a) "Both live near/in water and are reptile family members"; (b) "They are both not mammals"; (c) "They're both amphibians and can go underwater and stay underwater, and can both go on land. They both like bugs."
A final set of studies on this general topic examined how college and high school students respond when their prior knowledge of taxonomic relationships conflicts with evolutionary information provided in rectangular format cladograms (Novick & Catley, 2013b). In two studies, conducted with college and high school students respectively, we presented students with matched pairs of cladograms that depicted an identical pattern of relationships among either familiar or unfamiliar taxa. When the taxa were familiar, the cladograms showed (correct) relationships that conflicted with students' prior knowledge. For example, one such cladogram showed that mushrooms are more closely related to animals than they are to plants, contradicting folkbiological taxonomy that mushrooms are plants. Students answered evolutionary relationship questions about both cladograms in each matched pair. For both student groups, accuracy was higher when the cladograms depicted relationships among unfamiliar rather than familiar taxa. In addition, students were more likely to provide prior knowledge explanations for their responses (e.g., "mushrooms are plants") when the cladograms involved familiar taxa. These effects were larger for high school students.
An additional study in Novick and Catley (2013b) examined college students' willingness to include birds in the reptile category (which is where they belong) as a function of the strength of the supporting evidence. Even with salient visual evidence in the cladogram supporting this grouping, approximately half the students resisted this classification. On the positive side, students did at least choose a coherent definition of reptiles. For example, when they excluded birds from the category, they also excluded crocodiles, to which birds are most closely related. Evidently, the strength of many students' prior belief that birds are not reptiles is greater than their prior belief that crocodiles are reptiles.
Other research. Some ability to comprehend deep time is a prerequisite for understanding macroevolution. An early project (Catley & Novick, 2009) examined college students' knowledge of deep time in the context of seven major historical and evolutionary events (e.g., the age of the Earth, the emergence of life, the appearance of a pre-modern human -- Homo habilis). Subjects provided startlingly large time ranges for all questions, ranging over several orders of magnitude (e.g., from 1000 to 600 billion years ago for when most dinosaurs became extinct), coupled with a strong tendency to underestimate how long ago the events occurred. Converting absolute time estimates to relative time estimates allowed students' knowledge of the spacing of the events to be examined and also provided a clearer picture of their patterns of over and underestimation. The results of this study suggest that many students are without an effective conceptual framework to make sense of very large time frames. Although there were no consistent differences in the accuracy of students' responses as a function of their biology background, the weaker background students showed greater variability, providing more time estimates at both the low and high extremes.
Novick, L. R., Catley, K. M., & Schreiber, E. G. (2013). Fostering 21st Century Evolutionary Reasoning in Undergraduates: A Research-Based Approach to Teaching Tree Thinking. Manuscript in Preparation.
Novick, L. R., & Catley, K. M. (2013b). When Relationships Depicted Diagrammatically Conflict with Prior Knowledge: An Investigation of Students' Interpretations of Evolutionary Trees. Manuscript under revision for an invited resubmission.
Phillips, B. C., Novick, L. R., & Catley, K. M. (2013). The Great Chain of Being: How Diagram Design Influences Students' Reasoning About Human Evolution. Manuscript under review.
Novick, L. R., Pickering, J., MacDonald, T., Diamond, J., et al. (2011). Depicting the Tree of Life in Museums: Guiding Principles from Psychological Research. Manuscript under review.
Catley, K. M., Phillips, B. C., & Novick, L. R. (in press). Snakes and eels and dogs! Oh, my! Evaluating high school students' tree-thinking skills: An entry point to understanding evolution. Research in Science Education.
Novick, L. R., & Catley, K. M. (2013a). Reasoning about evolution's grand patterns: College students' understanding of the tree of life. American Educational Research Journal, 50, 138-177.
Novick, L. R., & Catley, K. M. (2012). Assessing students' understanding of macroevolution: Concerns regarding the validity of the MUM. International Journal of Science Education, 34, 2679-2703.
Phillips, B. C., Novick, L. R., Catley, K. M., & Funk, D. J. (2012). Teaching tree thinking to college students: It's not as easy as you think. Evolution: Education and Outreach, 5, 595-602.
Novick, L. R., Stull, A. T., & Catley, K. M. (2012). Reading phylogenetic trees: Effects of tree orientation and text processing on comprehension. BioScience, 62, 757-764.
Catley, K. M., Novick, L. R., & Funk, D. J. (2012). The promise and challenges of introducing tree thinking into evolution education. In K. Rosengren, E. M. Evans, S. Brem, & G. Sinatra (Eds.), Evolution Challenges: Integrating Research and Practice in Teaching and Learning about Evolution. New York, NY: Oxford University Press.
Novick, L. R., Shade, C. K., & Catley, K. M. (2011). Linear versus branching depictions of evolutionary history: Implications for diagram design. Topics in Cognitive Science, 3, 536-559.
Novick, L. R., Catley, K. M., & Funk, D. J. (2011). Inference is Bliss: Using Evolutionary Relationship to Guide Categorical Inferences. Cognitive Science, 35, 712-743.
Novick, L. R., Catley, K. M., & Funk, D. J. (2010). Characters are key: The effect of synapomorphies on cladogram comprehension. Evolution: Education and Outreach, 3, 539-547.
Morabito, N., Catley, K. M., & Novick, L. R. (2010). Reasoning about evolutionary history: The effects of biology background on post-secondary students' knowledge of most recent common ancestry and homoplasy. Journal of Biological Education, 44, 166-174.
Catley, K. M., Novick, L. R., & Shade, C. K. (2010). Interpreting evolutionary diagrams: When topology and process conflict. Journal of Research in Science Teaching, 47, 861-882.
Catley, K. M., & Novick, L. R. (2009). Digging deep: Exploring college students' knowledge of macroevolutionary time. Journal of Research in Science Teaching, 46, 311-332.
Catley, K. M., & Novick, L. R. (2008). Seeing the wood for the trees: An analysis of evolutionary diagrams in biology textbooks. BioScience, 58, 976-987.
Novick, L. R., & Catley, K. M. (2007). Understanding phylogenies in biology: The influence of a Gestalt perceptual principle. Journal of Experimental Psychology: Applied, 13, 197-223.
Novick, L. R. (2006). The importance of both diagrammatic conventions and domain-specific knowledge for diagram literacy in science: The hierarchy as an illustrative case. In D. Barker-Plummer, R. Cox, & N. Swoboda (Eds.), Diagrams 2006, LNAI 4045 (pp. 1-11). Berlin: Springer-Verlag.
Novick, L. R., & Catley, K. M. (2006). Interpreting hierarchical structure: Evidence from cladograms in biology. In D. Barker-Plummer, R. Cox, & N. Swoboda (Eds.), Diagrams 2006, LNAI 4045 (pp. 176-180). Berlin: Springer-Verlag.